Process for crimping difficultly crimpable fibers



3,335,477 PROCESS FOR CRIMPlNG DIFFICULTLY CRIMPABLE FIBERS Harold Edward Arnold, Kinston, N.C., assignor to E. l. du Pont de Nemonrs and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Apr. 20, 1965, Ser. No. 449,624 6 Claims. (Cl. 2872) This invention relates to highly crimped, high-denier fibers and more particularly to a crimping process for increasing the frequency of crimp in high-denier fibers.

It is well-known to employ stufiing-box crimpers such as that described in US. Patent No. 2,311,174 to crinkle continuous filament fibers. The crinkled, or crimped fibers may then be employed as a bundle of continuous filaments or may be cut to staple length for processing on one of the known staple processing systems such as the cotton system, worsted system, garnetter, etc. to yield structures resembling those of natural fibers in bulk and tactility.

An object of this invention is to provide a process for the high frequency crimping of difiicultly crimpable continuous filaments. Another object is to provide a process for crimping of high denier continuous filaments in a stufiing box to increase the crimp frequency. Other objects will appear hereinafter.

The objects of this invention are accomplished, in general, by a process for increasing the frequency of stufiing box crimp in difiicultly crimpable continuous filaments which comprises admixing at least by weight, based upon the total weight of continuous filaments, of easily crimpable continuous filaments with the difiicultly crimpable continuous filaments to form a blend and thereafter crimping the blend in a stufiing box crimper. The term easily crimpable continuous filaments is meant to define continuous filaments which, under the same operating conditions in a stufiing box crimper, have a crimp frequency of at least 1.3 times that of the difficultly crimpable continuous filaments. In the preferred embodiment, the diflicultly crimpable continuous filaments are continuous filaments having a denier per filament of at least 10; and the easily crimpable continuous filaments are continuous filaments which have a denier per filament of less than 10. More specifically, it is preferred to have a denier range of 30 to 50 for the difiicultly crimpable continuous filaments and a denier range of 2 to 7 for the easily crimpable continuous filaments.

Although it is understood that the invention is not to be limited by theoretical considerations, it is hypothesized that Eulers formula for column collapse under a critical load applies to the step of crimping wherein the column (fiber bundle) is loaded to the point of collapse in a stufiing box. Thus, P=1r2EI/1 states that the critical loading for collapse of a column (P) equals the product of a constant, the modulus of elasticity (E), and the moment of inertia (I) of the column divided by the square of its length. With a given polymeric composition comprising a range of fiber deniers and a crimper of given geometry, the modulus of elasticity and column length remain relatively constant. It is apparent, therefore, that in this case the force required to bring about column collapse will vary as the moment of inertia of the filament, which is approximately proportional to the fourth power of the filament diameter (this is strictly true only in the special case where the filaments are circular in cross-section). Although column collapse as hereinbefore described presumes no lateral or bending forces which cooperate to encourage buckling, it is theorized that the easily crimpable continuous filaments do in fact impart a lateral force on neighboring more 3,335,477 Patented Aug. 15, 1967 difiicultly crimpable continuous filaments to force an earlier collapse.

The following examples will serve to illustrate the invention, although they are not intended to be limitative. The examples were carried out using a stufiing box crimper similar to that described in United States Patent No. 2,311,174, using conditions known to produce the maximum obtainable crimp frequency. The amount of closing force applied to the hinged gate which restricts egress of the crimped continuous filaments from the stufiing box was maintained at the maximum operable force. The force is determined by gradually increasing the gate pressure during normal operation until the crimper jams, i.e., until the feed rolls are no longer able to force additional tow of continuous filaments into the stufiing box. Once such force is determined, the maximum operable force is chosen to be just below the determined force. The determinations of the crimp frequency is made by straightening a length of crimped tow sufliciently to count the individual crimps, extending the tow under a load sufiicient to remove all crimp and measuring the length of section in which the crimp was counted. Crimp frequency is reported in crimps per extended inch (c.p.i.) calculated by the following formula:

c.p.i.

Poly(ethylene terephthalate) of 0.5 intrinsic viscosity is melt spun to 104 filaments per spinneret substantially in accord with the process described in United States Patent No. 2,918,346. Approximately 200 such ends are combined to form a tow which is drawn 4.1 X (to 410% of its original length) by a process substantially as described in the aforementioned patent. The tow is dried and relaxed on a continuous-belt with circulating air maintained at C.

The tow is then crimped in the stufling box crimper. The crimped tow has a denier-per-filament (d.p.f.) of 40 and a total denier of 840,000; tenacity is 2.7 g.p.d.; elongation at the break is 62%, and shrinkage at 196 C. in dry air is 7.1%. The resulting crimped tow has an average crimp frequency of 4.1 per inch (c.p.i.), with 20 determinations being made which ranged from 3.3- 4.5 c.p.i.

Example 2 Example 1 is repeated in all essential respects, except that the tow is blended with varying amounts of a 4.75 d.p.f. poly(ethylene terephthalate) tow, whose total denier is varied so as to result in the desired weight percent lower denier-per-filament fiber in the tow to be crimped. Blending of the two tows is accomplished in each case by arranging individual spun ends in an alternating pattern as they are fed to the drawing step, thereby accomplishing a reasonably uniform distribution of the low denier per filament product in the total.

Characterization of the crimp of the fiber blends is illustrated in Table I:

As can be seen from Example 2, the average crimp frequency increases as increasing amounts of the smaller denier continuous filaments are added to the fiber blend. More significantly, however, is the fact that the minimum crimp frequency also increases. This illustrates that the higher denier filaments are being crimped to a higher frequency.

There is no upper limit with respect to the amount of the easily crimpable continuous filaments in the fiber blend. However, since the resulting crimped tow is not separated into its different component continuous filaments, a practical upper limit may be necessitated by specifications for the use to which the end product will be put. Additionally, the method by which the fiber blend is formed is not critical although it is preferred to have a uniform blend.

With regard to the stufling box crimper and its operation, it should be obvious that the particulars of the design are not critical. Also, the operating conditions of the crimper may be varied as desired. The examples were run at the optimum conditions for producing maximum crimp frequency to illustrate the extent of the increase in the crimp frequency by utilizing the process of this invention. Depending upon the desired crimp frequency, the operating conditions may be varied.

The examples utilized continuous filaments prepared from polyethylene terephthalate, this being the bestknown commercial polyester fiber. However, it should be obvious that other polyesters could be substituted with substantially equivalent results being had. Moreover, although it is preferred to utilize the same polymer to prepare both types of continuous filaments, there is no necessity that the same polymer be used. In fact, the characteristics desired in the crimped product might call for the use of two different polymers.

Additionally, the examples illustrate the practice of this invention by using easily crimpable continuous filaments of smaller denier to increase the crimp frequency of larger denier continuous filaments. It should be noted that other routes to easily crimpable continuous filaments could be advantageously utilized. For example, continuous filaments of intermediate denier per filament having a low modulus of elasticity or which change more rapidly in modulus when heated could be used. In this last instance, the heat could be supplied by contact with steam during the crimping, for example.

The process of this invention provides a simple method for increasing crimp frequency in relatively high denier continuous filaments. This increased frequency finds particular utility when the crimped tow is used for stufiing materials. The higher frequency of the crimped tow gives improved ability to yield appreciably under small loads but to resist bottoming" under large loads. This is an important characteristic of premium stufiings.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is:

1. The process for increasing the frequency of stuffing box crimps in difficultly crimpable continuous filaments which comprises admixing at least by weight, based upon the total weight of the continuous filaments of easily crimpable continuous filaments with said difiicultly crimpable continuous filaments to form a blend and thereafter crimping said blend in a stuifing box crimper whereby the crimping of the said easily crimpable continuous filaments imparts a lateral force on the said difficultly crimpable continuous filaments and thereby assists in the higher frequency crimping of the said diflicultly crimpable continuous filaments.

2. The process for increasing the frequency of stufiing box crimps in difiicultly crimpable continuous filaments which comprises admixing from about 10 to about 50% by weight, based upon the total weight of the continuous filaments of easily crimpable continuous filaments with said ditficultly crimpable continuous filaments to form a blend and thereafter crimping said blend in a stuffing box crimper whereby the crimping of the said easily crimpable continuous filaments imparts a lateral force on the said diificultly crimpable continuous filaments and thereby assists in the higher frequency crimping of the said difficultly crimpable continuous filaments.

3. The process for increasing the frequency of stufiing box crimps in first continuous filaments having a denier per filament of at least 10 which comprises admixing at least 10% by weight, based upon the total weight of continuous filaments of second continuous filaments having a denier per filament of less than 10 with said first continuous filaments to form a blend and thereafter crimping said blend in a stufiing box crimper whereby the crimping of the said second continuous filaments imparts a lateral force on the said first continuous filaments and thereby assists in the higher frequency crimping of the first continuous filaments.

4. The process for increasing the frequency of stuffing box crimps in first continuous filaments having a denier per filament of at least 10 which comprises admixing from about 10 to about 50% by weight, based upon the total weight of continuous filaments of second continuous filaments having a denier per filament of less than 10 with said first continuous filaments to form a blend and thereafter crimping said blend in a stuffing box crimper whereby the crimping of the said second continuous filaments imparts a lateral force on the said first continuous filaments and thereby assists in the higher frequency crimping of the first continuous filaments.

5. The process for increasing the frequency of stufling box crimps in first continuous filaments having a denier per filament range of from about 30 to about 50 which comprises admixing at least 10% by weight, based upon the total weight of continuous filaments, of second continuous filaments having a denier per filament range of from about 2 to about 7 with said first continuous filaments to form a blend and thereafter crimping said blend in a stufiing box crimper whereby the crimping of the said second continuous filaments imparts a lateral force on the said first continuous filaments and thereby assists in the higher frequency crimping of the first continuous filaments.

6. The process for increasing the frequency of stufiing box crimps in first continuous filaments having a denier per filament of about 40 which comprises admixing from about 10 to about 50% by weight, based upon the total weight of continuous filaments, of second continuous filaments having a denier per filament of about 4.75 with said first continuous filaments to form a blend and thereafter crimping said blend in a stufiing box crimper whereby the crimping of the said second continuous filaments imparts a lateral force on the said first continuous filaments and thereby assists in the higher frequency crimping of the first continuous filaments.

References Cited UNITED STATES PATENTS 2,311,174 2/1943 Hitt 2872 3,009,310 11/1961 Murchie et al. 2872 3,046,724 7/1962 Ward 57140 MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Examiner. 

1. THE PROCESS FOR INCREASING THE FREQUENCY OF STUFFING BOX CRIMPS IN DIFFICULTLY CRIMPABLE CONTINUOUS FILAMENTS WHICH COMPRISES ADMIXING AT LEAST 10% BY WEIGHT, BASED UPON THE TOTAL WEIGHT OF THE CONTINUOUS FILAMENTS OF EASILY CRIMPABLE CONTINUOUS FILAMENTS WITH SAID DIFFICULTLY CRIMPABLE CONTINUOUS FILAMENTS TO FORM A BLEND AND THEREAFTER CRIMPING SAID BLEND IN A STUFFING BOX CRIMPER WHEREBY THE CRIMPING OF THE SAID EASILY CRIMPABLE CONTINUOUS FILAMENTS IMPARTS A LATERAL FORCE ON THE SAID DIFFICULTLY CRIMPABLE CONTINUOUS FILAMENTS AND THEREBY ASSISTS IN THE HIGHER FREQUENCY CRIMPING OF THE SAID DIFFICULTLY CRIMPABLE CONTINUOUS FILAMENTS. 